The move protocol basically offers a player the choice to either start a new group, or grow any or all existing ones, posing a dilemma between sowing and growing. It also has an embedded balancing mechanism.
The diagram shows a position in which white resigned. Black's last move (move 21, growing all his groups by one stone) is indicated.
You can find this game among the example games: http://mindsports.nl/index.php/arena/sygo/634-example-games
Sygo is played on a standard goban. There are two players, Black and White. Both have a sufficient number of bi-colored stones. At the start of the game the board is empty.
- A group consists of one stone (by definition) or two or more orthogonally connected like-colored stones.
- White moves first. On his turn a player may either put a stone on a vacant cell, not connected to a like-colored group, thereby creating a new group, or grow any or all of his groups by one stone.
Moving is not compulsory: a player may pass without losing the right to move next turn.
- A stone connecting two or more different groups is considered to have grown all of them. A player may only grow at groups as they exist at the beginning of his turn, and no such group may grow more than one stone in that particular turn.
- Turn order balance
If, and only if, neither player has grown yet, then black may grow any or all of his groups followed by a single stone placement, in the same turn.
The orthogonally adjacent vacant points of a group constitute its liberties.
- If a placement or growing move does not result in a capture, it may never result in the stone or group of the moving player having no liberties itself. In other words: suicide is illegal.
- If the placement of a single stone results in an opponent's group losing its last liberty, then this group is reversed immediately to unite its captors in one group. This marks the end of the move. If the resulting group has no liberties either, then the move is suicidal and therewith illegal.
- If the growth of a group results in an opponent's group losing its last liberty, then this group is reversed immediately to unite its captors in one group. Such a group may not grow any further in the same turn. If the resulting group has no liberties either, then the move is suicidal and therewith illegal.
The stone placed or the group grown to effectuate the capture, may at the moment of placement (growth) have no liberties itself, but the resulting capture unites the captors in one group that, if alive, unites the captors in liberty.
Top left black has grown at E19 and now may not grow at C18 because the original group D/E18 would had two new stones adjacent to it. For the same reason black cannot, in one turn, capture the white stones top right.
Middle left black may grow at the marked point. It is true that he thus does make contact with a group that already did grow (the marked black stone), but none of the original groups has more than one new stone adjacent to it. For the same reason black can, in one turn, capture the white stones middle right.
Bottom left white may capture at A1 and the three black men are reversed immediately. That constitutes the beginning and the end of the turn. Black may thereafter capture the eight white stones by growing at the marked points.
Bottom right is a seki of sorts: neither can grow at R1 without allowing the opponent the possibility of capturing the resulting group with a single placement. Of course the opponent may have bigger problems to deal with, requiring growth instead of placement, so growing at R1 may well serve a tactical purpose.
Top left white may not grow at D19: that would be suicide. Top right, white can neither place at T19, nor grow at R19: both would be suicide.
Bottom left white cannot capture by growing at the marked point, because the resulting white group would have no liberties, making the move suicidal. Bottom right shows a ko isn't possible. Even if black would have had a legitimate reason to make a placement at Q3, a capture at R3 would not open a ko but close Q3.
Note: the Sygo board has coordinates A-S, that is: including I and J. Here the regular goban is used for convenience.
The game ends by one player's resignation or when players pass on successive turns. The winner is now the player with the largest terrirory, counted as stones plus surrounded vacant territory. In a seki only vacant points that are completely surrounded by one player count.
On rare occasions Sygo may end in a draw.
Sygo at Mindsports: http://mindsports.nl/index.php/arena/sygo/
Turnbased play: http://mindsports.nl/index.php/players-section
Othelloanian capture in Go variants: http://mindsports.nl/index.php/arena/sygo/621-othellonian
Sygo at wiki (Chinese): http://ppt.cc/jGxW
Sygo at BBG: http://www.boardgamegeek.com/boardgame/106350/sygo